1. Field of the Invention
The present invention relates generally to apparatus and method for reforming the bottoms of containers. More particularly, the present invention relates to apparatus and method for doming the bottoms of beverage container bodies that are drawn and ironed.
2. Description of the Related Art
Commonly, in the production of beverage containers, a cup is drawn, and then the cup is redrawn and ironed in a machine called a bodymaker. In the bodymaker, a ram, moving along a longitudinal and horizontal ram axis, functioning as a die punch, carries the cup through a first die wherein it is redrawn. Then, the ram carries the redrawn cup successively through a plurality of ironing dies, the metal of the sidewall being progressively thinned, and the height of the container body, or container shell, being successively increased.
Typical apparatus for performing these redrawing and ironing steps is taught by Grigorenko in U.S. Pat. No. 3,733,881, issued May 22, 1973.
Further, it is common practice to form the bottom of the container body, or container shell, with a contour that increases the static dome reversal pressure of the container, the objective being to obtain the greatest dome reversal pressure for a given metal thickness. More particularly, the objective has been to optimize the bottom contour, thereby both minimizing stock thickness and material cost, while maintaining the required static dome reversal pressure.
Various bottom contours have been used through the years. Presently, the most common bottom contour includes a spherical dome that curves upwardly into the container. A bottom contour that achieves increased bottom strength is taught by Baldwin in U.S. patent application Ser. No. 07/505,618, filed Apr. 6, 1990, of common ownership with the present patent application.
More recently, the primary emphasis on bottom strength has shifted from dome reversal pressure to drop resistance of the container as beverage bottlers have attempted to reduce their costs by eliminating case cartons, and, instead, have shrink wrapped case lots of beverages. This elimination of the case carton, and consequent elimination of the impact resistance of the cardboard carton, has resulted in an urgent need for container bottoms with increased drop resistance.
Presently, the drop resistance of beverage containers is determined by a drop test in which filled containers are dropped onto a steel plate from progressively increased heights; and the drop resistance is given as the cumulative sum of the drop heights prior to container failure.
Jentzsch et al. in U.S. patent applications Ser. Nos. 07/600,943 and 07/600,943, both filed Oct. 22, 1990, and both of common ownership with the present patent application, provide beverage containers with increased dome reversal pressures as well as increased cumulative drop height resistances.
Various types of tooling have been used for doming the bottoms of the beverage containers. Generally, the domer apparatus has been attached to the bodymaker coaxially with the ram thereof. Thus, after the ram has redrawn the cup, and after the ram, functioning as a die punch, has carried the redrawn cup through a progression of ironing dies to form a container shell, the ram then cooperates with the domer apparatus to form a recessed dome in the bottom of the container shell.
Paramonoff, in U.S. Pat. No. 3,771,345, issued Nov. 13, 1973, teaches a swinging-door mechanism for attaching domer apparatus to a bodymaker that is manufactured by Standun, Inc. of Compton, Calif.
In many prior art designs, the domer apparatus includes two dies, an inner die, and an outer die that is disposed circumferentially around the inner die. Both the inner and outer dies cooperate with the ram of the bodymaker. As the ram carries a container shell into contact with the domer apparatus, the outer die engages the bottom of the container shell radially outward of the area in which the bottom is to be domed. Then, as this outer die is allowed to be resiliently moved along with the container shell and the ram, the inner die is engaged, thereby forming a domed bottom in the container shell.
Preferably, the inner die is resiliently held in a longitudinal working position, as well as the outer die being resiliently held in a working position. Thus, in the event that a container shell becomes crumpled between the ram and the inner die, the inner die will move away from the ram without damaging either the bodymaker or the domer apparatus.
Prior art designs in which both the inner and outer dies are moveable and resiliently urged into their respective working positions include: Paramonoff, U.S. Pat. No. 3,771,345, issued Nov. 13, 1973; Maeder et al., U.S. Pat. No. 4,289,014, issued Sep. 15, 1981; Pulciano et al., U.S. Pat. No. 4,620,434, issued Nov. 4, 1986; Bulso, Jr. et al., U.S. Pat. No. 4,732,031, issued Mar. 22, 1988; Johansson et al., U.S. Pat. No. 4,790,169, issued Dec. 13, 1988; and Weishalla, U.S. Pat. No. 4,930,330, issued Jun. 5, 1990.
Of the above-listed prior art patents in which both the inner and outer dies are resiliently held in their respective working positions, Paramonoff, Maeder et al., Pulciano et al., and Bulso, Jr. et al. use a fluid actuator for resiliently positioning each of the two dies. Of these four prior art patents, Maeder et al. use external fluid actuators of the bag type; but the other three use internal fluid actuators of the piston type.
Of the remaining prior art patents in which both dies are resiliently positioned, Johansson et al. use springs for both dies, and Weishalla uses a fluid actuator for resiliently positioning the outer die, and a urethane spring for positioning the inner die.
Also of interest are Elert et al., U.S. Pat. No. 4,372,143, issued Feb. 8, 1983, and Williams, U.S. Pat. No. 4,733,550, issued Mar. 29, 1988. In both of these patents, a subassembly is provided that includes both the inner and outer dies. A first air spring is used to resiliently bias this subassembly, including the inner and outer dies thereof, toward the ram. If a container should become crumpled between the ram and the inner die, this first air spring allows the subassembly to move away from the ram, thereby preventing damage to the domer tooling and/or to the can maker.
A second air spring is included within the subassembly and is used to bias the outer die toward the ram. The second air spring, being smaller in diameter, provides a smaller resilient force than the first air spring. This smaller resilient force allows the outer die to move with the ram during the dome forming operation.
In these designs of Elert et al. and Williams, the smaller air spring, which is actuated with each cycle of the ram, is disposed inside the subassembly. Thus, a disadvantage of these designs is that extensive disassembly of the domer tooling is required for replacement of the air spring that operates the most frequently and that is most subject to failure.
Bodymakers typically operate at speeds of two hundred containers or more per minute; so the domer apparatus is subjected to rapid, repeated stresses. Further, as is true in any high production manufacturing process, it is important to reduce downtime; so a design objective is to be able to inspect and repair the domer apparatus in a minimum amount of time. Further, in order to minimize repair time, it is highly advantageous to be able to perform most repairs without removing the domer apparatus from the bodymaker. By avoiding the necessity of removing the domer apparatus from the bodymaker, time required to realign the domer apparatus to the bodymaker is obviated.
Therefore, the present invention incorporates the design objective of withstanding rapid and repeated stresses, reduction of mass of moving parts with a consequent reduction in inertial forces, elimination of heat sensitive and troublesome rubber seals, ability to dissipate heat generated by rapid operation, ability to inspect and repair the domer apparatus in a minimum amount of time, and ability to make most repairs without disassembly from the bodymaker.
Although no improvement in container strength was anticipated, and although the reasons are not readily apparent, the present invention increases the dome reversal pressures of containers by two to five pounds per square inch without any changes in the design of the dome or in the metal thickness. It is postulated that the reason for this unexpected improvement in container strength may be due to the lower operating mass of the parts associated with movement of the outer die and a resultant reduction in acceleration forces.